Implement a binary sensor to expose the connectivity status

[palazzem]

Is your feature request related to a problem? Please describe.
If the main unit is not connected, automations may wrongly trigger (e.g. blinders are closing assuming the integration will turn off the alarm).

Describe the solution you'd like
Expose a sensor that users can use in their integrations to be sure they can safely trigger an automation without the alarm triggering.

Describe alternatives you've considered
n/a

Additional context
n/a

[palazzem]

Requires palazzem/econnect-python#146